A conventional recorder for an optical master disk comprises two optical systems i.e. a fixed optical system and a movable optical system, and needs a large recording light source such as a gas laser. Accordingly, in the recorder, the fixed optical system is separated from the movable optical system.
However, the development of a semiconductor laser and the combination of a non-linear optical element with the semiconductor laser enable a recording light source to be miniaturized. Therefore, this has allowed the movable optical system to accommodate the fixed optical system.
In general, a semiconductor laser tends to emit a light beam which diverges at different angles from a junction. As a result, the divergence angle parallel to the junction is different from the divergence angle orthogonal to the junction, so that the laser provides a light beam having an oval shape in a cross section. Therefore, it is necessary to pass the light beam through a shaping prism to correct the shape of the light beam.
FIG. 1 shows one example of a shaping prism. The shaping prism 3 is made from a material having a predetermined refractive index into a predetermined shape. If a light beam having an oval shape enters the prism 3, the prism 3 functions to convert the oval shape of the light beam into a substantially circular shape.
However, when the light beam passes through the prism, the prism converts the shape of the beam, and simultaneously results in bending an optical path of the beam at a predetermined angle. Accordingly, the bending of the optical path causes the recorder to increase the length of the optical path and its size.